1,3-butadiene, the demand for which is increasing in petrochemical markets, is produced through a naphtha cracking process, a direct n-butene dehydrogenation reaction, or an oxidative n-butene dehydrogenation reaction, and is then supplied to a petrochemical market. Among them, the naphtha cracking process accounts for 90% or more of butadiene supply, but is problematic in that new naphtha cracking centers (NCCs) must be established in order to meet the increasing demand for butadiene, and in that other basic fractions, as well as butadiene, are excessively produced because the naphtha cracking process is not a process for producing only butadiene. Further, the direct n-butene dehydrogenation reaction is problematic in that it is thermodynamically disadvantageous, and in that high-temperature and low-pressure conditions are required because it is an endothermic reaction, so that the yield is very low, with the result that it is not suitable for a commercial process [L. M. Madeira, M. F. Portela, Catal. Rev., volume 44, page 247 (2002)].
The oxidative n-butene dehydrogenation reaction, which is a reaction for forming 1,3-butadiene and water by reacting n-butene with oxygen, is advantageous in that, since stable water is formed as a product, the reaction is thermodynamically favorable, and the reaction temperature can be lowered. Therefore, a process of producing 1,3-butadiene through the oxidative n-butene dehydrogenation reaction can be an effective alternative process for producing only butadiene. In particular, when a C4-raffinate-3 mixture or a C4 mixture containing impurities, such as n-butane and the like, is used as a supply source of n-butene, there is an advantage in that excess C4 fractions can be made into high value-added products. Specifically, the C4-raffinate-3 mixture, which is a reactant used in the present invention, is a cheap C4 fraction obtained by separating useful compounds from a C4 mixture produced through naphtha cracking. More specifically, a C4-raffinate-1 mixture is a mixture obtained by separating 1,3-butadiene from a C4 mixture produced through naphtha cracking, a C4-raffinate-2 mixture is a mixture obtained by separating iso-butylene from the C4-raffinate-1 mixture, and a C4-raffinate-3 mixture is a mixture obtained by separating 1-butene from the C4-raffinate-2 mixture. Therefore, the C4-raffinate-3 mixture or C4 mixture mostly includes 2-butene (trans-2-butene and cis-2-butene), n-butane, and 1-butene.
As described above, the oxidative dehydrogenation reaction of n-butene (1-butene, trans-2-butene, cis-2-butene) is a reaction for forming 1,3-butadiene and water by reacting n-butene with oxygen. However, in the oxidative dehydrogenation reaction of n-butene, many side reactions, such as complete oxidation, etc., are predicted because oxygen is used as a reactant. For this reason, it is very important to develop a catalyst which can suppress these side reactions to the highest degree and has high selectivity for 1,3-butadiene. Examples of catalysts currently used for the oxidative dehydrogenation reaction of n-butene include a ferrite-based catalyst [M. A. Gibson, J. W. Hightower, J. Catal., volume 41, page 420 (1976)/W. R. Cares, J. W. Hightower, J. Catal., volume 23, page 193 (1971)/R. J. Rennard, W. L. Kehl, J. Catal., volume 21, page 282 (1971)], a tin-based catalyst [Y. M. Bakshi, R. N. Gur'yanova, A. N. Mal'yan, A. I. Gel'bshtein, Petroleum Chemistry U.S.S.R., volume 7, page 177 (1967)], a bismuth molybdate-based catalyst [A. C. A. M. Bleijenberg, B. C. Lippens, G. C. A. Schuit, J. Catal., volume 4, page 581 (1965)/Ph. A. Batist, B. C. Lippens, G. C. A. Schuit, J. Catal., volume 5, page 55 (1966)/W. J. Linn, A. W. Sleight, J. Catal., volume 41, page 134 (1976)/R. K. Grasselli, Handbook of Heterogeneous Catalysis, volume 5, page 2302 (1997)] and the like.
Among them, the ferrite-based catalyst has a spinel structure of AFe2O4 (A=Zn, Mg, Mn, Co, Cu, and the like). It is known that the ferrite having such a spinel structure can be used a catalyst for an oxidative dehydrogenation reaction through the oxidation and reduction of iron ions and the interaction of oxygen ions and gaseous oxygen in crystals [M. A. Gibson, J. W. Hightower, J. Catal., volume 41, page 420 (1976)/R. J. Rennard, W. L. Kehl, J. Catal., volume 21, page 282 (1971)]. The catalytic activities of ferrite-based catalysts are different from each other depending on the kind of metals constituting the bivalent cation sites of the spinel structure. Among them, zinc ferrite, magnesium ferrite and manganese ferrite are known to exhibit good catalytic activity in the oxidative dehydrogenation reaction of n-butene, and, particularly, zinc ferrite is reported to have higher selectivity for 1,3-butadiene than other metal ferrites [F.-Y. Qiu, L.-T. Weng, E. Sham, P. Ruiz, B. Delmon, Appl. Catal., volume 51, page 235 (1989)].
It was reported in several patent documents that zinc ferrite-based catalysts were used in the oxidative dehydrogenation reaction of n-butene. Specifically, in relation to the fact that 1,3-butadiene is produced through the oxidative dehydrogenation reaction of n-butene using pure zinc ferrite made by a coprecipitation method, it was reported that the oxidative dehydrogenation reaction of 2-butene was conducted using a zinc ferrite catalyst having a pure spinel structure at 375° C., thus obtaining a yield of 41% [R. J. Rennard, W. L. Kehl, J. Catal., volume 21, page 282 (1971)]. Further, it was reported that 1,3-butadiene was obtained at a yield of 21% at 420° C. through an oxidative dehydrogenation reaction, in which 1-butene was used as a reactant and a zinc ferrite catalyst was used [J. A. Toledo, P. Bosch, M. A. Valenzuela, A. Montoya, N. Nava, J. Mol. Catal. A, volume 125, page 53 (1997)].
Further, methods of manufacturing a zinc ferrite catalyst, by which 1,3-butadiene can be produced at a higher yield through pre-treatment and post-treatment, performed in order to increase the activity of a zinc ferrite catalyst in an oxidative dehydrogenation reaction, was disclosed in several patent documents [F.-Y. Qiu, L.-T. Weng, E. Sham, P. Ruiz, B. Delmon, Appl. Catal., volume 51, page 235 (1989)/L. J. Crose, L. Bajars, M. Gabliks, U.S. Pat. No. 3,743,683 (1973)/J. R. Baker, U.S. Pat. No. 3,951,869 (1976)].
In addition to the above methods of manufacturing a zinc ferrite catalyst, in order to increase the activity of a catalyst in the oxidative dehydrogenation reaction of n-butene, the oxidative dehydrogenation reaction of n-butene was conducted using a catalyst in which a zinc ferrite catalyst is physically mixed with other metal oxides [W.-Q. Xu, Y.-G. Yin, G.-Y. Li, S. Chen, Appl. Catal. A, volume 89, page 131 (1992)].
The zinc ferrite catalyst, reported in the above patent documents, is single-phase zinc ferrite or a catalyst system including the single-phase zinc ferrite as a central component, and the zinc ferrite, which is a central component acting on the oxidative dehydrogenation reaction of n-butene, is chiefly prepared using a coprecipitation method. As a typical example of a method of preparing zinc ferrite using a coprecipitation method, there is a method of adding an aqueous zinc precursor solution and an aqueous iron precursor solution to an excess aqueous reductant solution [L. J. Crose, L. Bajars, M. Gabliks, U.S. Pat. No. 3,743,683 (1973)/J. R. Baker, U.S. Pat. No. 3,951,869 (1976)].
In addition to the methods of increasing the activity of the zinc ferrite catalyst through pre-treatment and post-treatment or mixing, clearly set forth in the above patent documents, as an attempt to increase the activity of the catalyst itself, a method of substituting zinc or iron, which is a component of zinc ferrite, with other metals has also been reported in patent documents. It was disclosed in this method that, in a catalyst in which other metals, instead of iron, are disposed at trivalent iron ion sites of ferrite having a spinel structure, the activity of the catalyst is changed due to the presence of the other metals. In particular, it was reported in a document that, when a catalyst substituted with chromium or aluminium was used, catalytic activity was increased [J. A. Toledo, P. Bosch, M. A. Valenzuela, A. Montoya, N. Nava, J. Mol. Catal. A, volume 125, page 53 (1997)].
In the oxidative hydrogenation reaction of n-butene, when the zinc ferrite catalyst substituted with other metals or the mixed-phase catalyst is used, high activity can be obtained in the production of 1,3-butadiene, compared to when a conventional zinc ferrite catalyst is used, but there is a problem in that it is difficult to synthesize the above catalyst, and it is also difficult to reproduce the above catalyst, and thus it is difficult to commercialize the above catalyst. Further, since a C4 mixture, which is a reactant used in the present invention, includes various components as well as n-butene, when the above catalyst is used, there is a problem in that catalytic activity and selectivity for 1,3-butadiene may be greatly changed due to side reactions.
The oxidative dehydrogenation reaction of n-butene has another problem in that, when a reactant includes n-butane in a predetermined amount or more, the yield of 1,3-butadiene is decreased [L. M. Welch, L. J. Croce, H. F. Christmann, Hydrocarbon Processing, page 131 (1978)]. Therefore, in the above conventional technologies, an oxidative dehydrogenation reaction is conducted using only pure n-butene (1-butene or 2-butene) as a reactant, thus solving such problems. In practice, reactants containing no n-butane are used even in commercial processes using a ferrite catalyst. As disclosed in the above patent documents, in the catalyst and process for preparing 1,3-butadiene from n-butene through an oxidative dehydrogenation reaction, since pure n-butene is used as a reactant, an additional process of separating pure n-butene from a C4 mixture is required, thus inevitably decreasing economic efficiency.
As described above, in the conventional catalysts and processes for preparing 1,3-butadiene through the oxidative dehydrogenation reaction of n-butene, 1,3-butadiene is prepared using pure n-butene as a reactant through a mixed-phase, substituted or modified zinc ferrite catalyst. However, an example in which 1,3-butadiene was prepared using a C4-raffinate-3 mixture or a C4 mixture including various components as well as n-butane having a high concentration on a pure single-phase zinc ferrite catalyst without performing additional pre-treatment or post-treatment and metal substitution procedure has never been reported.